Electric Engine-Cooling Fans

Electric engine-cooling fans are used on all transversely and some longitudinally mounted engines. Small, permanent-magnet, high-torque motors are used for this application. They are able to move large amounts of air independent of engine speed. Conventional electric cooling fan circuits incorporate a relay and engine-coolant temperature switch.

When engine coolant temperature increases above 230*F or 100*C, the cooling fan switch closes to energize the relay coil and switch the cooling fan motor ON. The coil is also energized to switch the cooling fan motor ON any time the air conditioning unit is ON. On some vehicles the temperature-switch circuit is hot at all times, allowing the fan to continue to cool the engine compartment and the radiator coolant even if the ignition switch is OFF. For this reason, you should always disconnect the fan motor when working under the hood near it in case it comes on without warning.

Cooling fan motors are also controlled by on-board computer-based electronic control module. A temperature sensor provides the input information used by the computer to determine the exact coolant temperature. Based on this information and other instructions programmed into it, the computer outputs signal that switches the fan circuit ON and OFF.

One advantage of this type of control circuit is that the computer may be programmed to turn the fan OFF. Automatically when the car is traveling at speeds above approximately 35 mi/h. This puts less load on the alternator. The fan is not normally needed when the car travels at road speeds because of forced air flowing across the radiator.